1. Technical Field
The present invention relates to ferroelectric memories and methods for manufacturing the same.
2. Related Art
For ferroelectric memories, the structure in which a ferroelectric capacitor is stacked on a selection transistor is known. A dielectric layer is provided between the ferroelectric capacitor and the selection transistor, and an electrical connection between them is made by a plug embedded in a contact hole in the dielectric layer. The plug is formed by forming a film of conductive layer that is a plug material inside the contact hole and on the dielectric layer, and the entire conductive layer is polished by using a chemical mechanical polishing (CMP) method or the like. However, in this case, a recess (concave section), which is caused by a difference in the polishing rate between the conductive layer and the surrounding dielectric layer, is generated in the conductive layer at the contact hole. If the recess is left remained, the ferroelectric capacitor cannot be formed on a flat surface, so that the stability in the manufacturing process may be damaged, and the reliability may possibly be lowered. It is noted that, in the process of manufacturing the ferroelectric capacitor, a process of oxidizing the ferroelectric layer is necessary, and therefore prevention of oxidation of the plug is required.
It is an object of the present invention to provide ferroelectric memories that can improve the reliability and methods for manufacturing the same.